The power grid is a distribution network for delivering power from suppliers to consumers. Traditionally, the electrical needs of consumers have been met by power companies distributing power through the grid. A power grid provides the majority of the power that is made available to a region. Power is generated at a location and distributed through the power grid to the surrounding areas. This power is distributed in the form of alternating current (AC) power, which is transmitted at very high voltages along power lines. The majority of the power transmitted through the grid is in three phases.
Power is transmitted in three phases to provide an even source of power which can be readily distributed over long distances with efficient wiring costs. Three-phase power is AC power that is transmitted along three separate power lines. Each line of power is in a different phase, with the phase of each power line shifted relative to the other two power lines by 120 degrees. These phases are shifted from each other to provide the consistency of a DC power source using AC power.
Three-phase power is a standard method for power distribution throughout the world. In the United States, power is distributed in three phases, but the majority of all homes are run on a single phase. The three-phase power is split into single phases at a transformer, where the voltages are stepped down and the phases are split up. However, some homes and businesses are configured to receive three-phase power.
FIG. 1 illustrates energy usage in a home 105 wired for three-phase power from the power grid. The home 105 may be any site where power is consumed or produced, such as an industrial building or an isolated solar panel installation. FIG. 1 shows three power lines 125, 130, and 135, the home 105, a load 160, and a power grid 120. The three power lines 125, 130, and 135 provide power from the grid 120 to the load 160 in the home 105 in three different phases shown in graphs 145, 150, and 155 respectively.
The load 160 for the home 105 is powered by the three power lines 125, 130, and 135 supplied by the power grid 120. The graphs 145, 150, and 155 of the three phases show that the phases of the power lines 125, 130, and 135 are shifted in time with a phase difference of one-third of a cycle or 120 degrees. The phase difference provides power such that one of the three phases will be reaching its peak at three different points of a single cycle of a particular power line, which allows an AC power source to provide the consistency of a DC power source. Some alternative power generators, such as solar panels, provide DC power, but in order to be used with the grid, the DC power source must be converted to AC power.
Solar panels have become an increasingly common alternative source of energy. With installations of varying sizes, consumers have also become producers, resulting in a multitude of power producers, rather than a single producer. Consumers are able to produce their own power, reducing their reliance on the power companies. Due to the nature of solar power energy being more readily available during the day, residential customers may be producers during the day, but consumers during the night as the needs of a particular site change throughout the day. As the amount of power that the solar installation inject into the grid and the needs of the consumer change throughout the day, additional power may need to either be drawn from the grid or returned to the grid. However, in order for the solar installation to inject power into the grid, the DC power generated by the solar panels on the installation needs to be converted to AC power in a form similar to the power provided by the grid.
The conversion of power from solar panels from DC power to AC power is often done using inverters. Typically, the solar panels are wired in series and then connected with high-voltage cables to connect the DC power to an inverter. These solar panel installations use a single, large inverter to convert the generated power into power which can be used in the home or fed back into the grid.
FIG. 2 illustrates energy usage in a home 205 wired for three-phase power where power supplied for the home 205 is supplied from solar panels 215 which provide DC power to a single inverter 262. Similarly to FIG. 1, the three power lines 225, 230, and 235 provide power to the load 260 of the home 205. In addition, FIG. 2 shows solar panels 215 and inverter 262. The solar panels 215 provide DC power to the inverter 262 which converts the DC power and provides AC power to the three power lines 225, 230, and 235. Single inverter installations require a large inverter as well as heavy, high-voltage cabling to bring the DC power to the AC inverter.
In recent years there has been an emergence of interest in module-integrated electronics. The solar micro-inverter in particular has been noted as a product that has a number of benefits over the existing conventional solutions. Micro-inverters are smaller inverters which are installed on or near the solar panels themselves. Rather than a single inverter for inverting all of the power provided by an installation, micro-inverters invert the power of one or a few solar panels and provide AC power at the source panels. Micro-inverters provide many benefits over traditional inverters. These benefits include: improved energy harvest over the lifetime of the installation, particularly in scenarios of shading or other causes of mismatch in solar photovoltaic (PV) installations and low voltage DC (less than 80V from a single panel), which is safer and significantly reduces arcing faults. Additional benefits of an energy harvesting system based on micro-inverters also include the ability to pin point failures or problems with solar panels (or solar modules), and the ease of scalability when adding panels to an installation. The installation process itself is also extremely easy and can be considered as a plug and play method.